This invention relates to a novel class of Mannich base condensation products that act as potent soot dispersants in lubricating oil compositions. The invention is further directed to lubricating oil compositions containing said soot dispersants.
Lubricating oil compositions comprise a major amount of a base oil and additives that improve the performance and increase the useful life of the lubricant. Nitrogen-containing dispersants are commonly used lubricant additives. The function of a dispersant is to maintain in suspension within the oil, insoluble materials formed by oxidation and other mechanisms during use of the oil, to prevent sludge flocculation and precipitation of the insoluble materials. Another function of the dispersant is to reduce the agglomeration of soot particles, thus reducing increases in the viscosity of the lubricating oil upon use. Crankcase lubricants providing improved performance, including improved soot dispersancy, have been continuously demanded.
To improve the sludge dispersing characteristic of lubricating oils, industry has moved to the use higher molecular weight materials, which have superior sludge dispersing properties compared to lower molecular weight materials, and have used such high molecular weight dispersants in ever increasing amounts. However, dispersants are expensive, may contain residual levels of chlorine, which leads to problems with the disposal of used lubricants, do not blend well in lubricants also containing overbased detergents and contain a high level of basic amine, which causes the deterioration of seals within the engine during service. In addition, high molecular weight dispersants, even when used in greater amounts, do not provide sufficient soot dispersing properties, particularly in high soot environments as are encountered with lubricating oils for heavy duty diesel engines. Therefore, it would be advantageous to be able to provide a lubricant with adequate soot dispersancy properties, and preferably, to do so using reduced amounts of high molecular weight dispersant.
U.S. Pat. No. 3,442,808 relates to lubricating oil additives prepared by reacting alkenyl succinic anhydride with a Mannich base condensation product prepared by condensing alkyl substituted phenol, formaldehyde and polyalkylene polyamine.
U.S. Pat. No. 3,458,495 relates to oxidation inhibitors and dispersant-detergent oil additives comprising the reaction product of one equivalent of a phosphosulfurized hydrocarbon and about 0.5 to 4 equivalents of an alkylene amino phenol. The phosphosulfurized hydrocarbons are prepared by reacting a terpene, a petroleum fraction or a 500 to 200,000 molecular weight C2 to C6 olefin polymer (including polymers of ethylene, propylene, butylene, isobutylene or isoamylene) and from 5 to 40 wt % of a sulfide of phosphorous. The alkylene amino phenol is prepared by a Mannich base condensation of aldehyde, alkylene polyamine and alkyl phenol.
U.S. Pat. No. 4,354,950 discloses a method of preparing Mannich base derivatives of hydroxyaryl succinimides of the formula: 
wherein R is hydrocarbyl of 25 to 200 carbon atoms, Rxe2x80x2 is H, alkyl or halogen, xe2x80x9cnxe2x80x9d is 2 or 3, xe2x80x9cmxe2x80x9d has a value of 1 to 5, Y is H or a methylene hydroxyaryl succinimide radical, xe2x80x9cxxe2x80x9d has a value of 1 to 2 when Y is H and a value of 1 when Y is a methylene hydroxyaryl succinimide radical. The above succinimides are formed in a stepwise reaction, e.g., by reacting a polyalkenyl succinic anhydride with an aminophenol to produce an intermediate N-(hydroxyaryl) hydrocarbyl succinimide, which is then reacted with an alkylene diamine and an aldehyde (e.g., formaldehyde) in a Mannich base reaction to produce the desired product. The resulting succinimides may be added to a base oil of lubricating viscosity to form lubricant concentrates and lubricating oil formulations.
U.S. Pat. Nos. 5,017,299; 5,186,851 and 5,345,002 describe Mannich base condensates of alkyl substituted hydroxy aromatic compounds with formaldehyde and an amine, wherein the alkyl-moiety of the aromatic compound is derived from ethylene alpha-olefin copolymer having a number average molecular weight of 300 to 10,000, and wherein at least 30% of the polymer""s chains contain a terminal ethenylidene unsaturation.
U.S. Pat. No. 5,580,484 describes a succinimide Mannich base condensate of an alkyl substituted hydroxy aromatic compound, an aldehyde and a xe2x80x9cheavy polyaminexe2x80x9d defined as a mixture of polyalkylenepolyamines comprising small amounts of lower polyamine oligomers, such as tetraethylene pentamine and pentahexamine, and a large majority of oligomers with 7 or more nitrogens and 2 or more primary amines per molecule, and a greater degree of branching compared to conventional polyamine mixtures. Again, the alkyl-moiety of the aromatic compound is described as being derived from a polymer backbone having a number average molecular weight of greater than 300.
In accordance with one aspect of the present invention, there are provided novel Mannich base condensates of hydroxy aromatic compounds, optionally substituted with one or more short-chain (C1-C20) hydrocarbyl moieties; an aldehyde; and an amine, wherein the combined number of carbon atoms in any optional hydrocarbyl substituents of the hydroxyaromatic moiety, the aldehyde, and the amine does not exceed 80.
In accordance with another aspect of the present invention, a lubricating oil composition is provided which comprises a base oil of lubricating viscosity and an effective amount of a soot dispersant which are Mannich base condensates of hydroxy aromatic compounds, optionally substituted with one or more short-chain (C1-C20) hydrocarbyl moieties; an aldehyde; and an amine, wherein the combined number of carbon atoms in any optional hydrocarbyl substituents of the hydroxyaromatic moiety, the aldehyde, and the amine does not exceed 80.
In accordance with still another aspect of the present invention, there is provided a lubricating oil composition or concentrate which comprises a base oil of lubricating viscosity and an effective amount of (1) a Mannich base condensate of a hydroxy aromatic compound, optionally substituted with one or more short-chain (C1-C20) hydrocarbyl moieties; an aldehyde; and a primary or secondary amine, wherein the combined number of carbon atoms in any optional hydrocarbyl substituents of the hydroxyaromatic moiety, the aldehyde, and the amine does not exceed 80, and (2) a high molecular weight nitrogen-containing dispersant.
Compared to the Mannich base materials of the prior art, the lower molecular weight materials of the invention provide lubricating oils with superior soot dispersing characteristics and, when used in combination with conventional high molecular weight nitrogen-containing dispersant, synergistically enhance the inherent soot dispersing properties of the high molecular weight dispersant. As an added benefit, the addition of the Mannich base materials of the present invention to a lubricating oil composition provides an antioxidancy credit.